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Telling Time by Sun and Water

Telling Time by Sun and Water

Long before anyone owned a watch, people needed ways to divide the day. Workers had to know when to start and finish, traders when to meet, and officials how long a speech should last. The earliest solutions relied on two things that were nearly always at hand: sunlight and water.

The simplest sundial is a stick pushed upright into the ground. As the sun moves across the sky, the stick's shadow swings slowly around it: long in the morning, short at midday and long again in the afternoon. By marking where the shadow fell, people could divide daylight into parts. Later sundials were carved from stone, with a raised pointer called a gnomon to cast the shadow and lines cut into the face to show the hours.

Sundials had an obvious drawback: they were useless at night and on cloudy days. To fill the gap, people in ancient Egypt and elsewhere developed water clocks. One early kind was a stone bowl with a tiny hole near the bottom. As water dripped steadily out, the level inside fell past marks on the inner wall, each showing that a certain amount of time had passed. Other water clocks worked the opposite way, measuring time by how quickly a container filled.

Neither method was perfect. The shadow's position at each hour shifted with the seasons, and water flowed faster when a bowl was full than when it was nearly empty, so the hours were not always equal. Clockmakers spent centuries refining their designs, adjusting the shapes of bowls and the markings on dials to make them more accurate.

Even so, these early devices changed the way people lived. For the first time, a day was not only light and dark but a series of measured hours that everyone could share.